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PubMed1984

Hemichloris antarctica, gen. et sp. nov. (Chlorococcales, Chlorophyta), a cryptoendolithic alga from Antarctica.

Hemichloris antarctica gen. et sp. nov. (Oocystaceae, Chlorococcales) is characterized by a single, articulated, pyrenoid-less, thick saucer-shaped chloroplast, which generally fills less than half of the cell periphery. Multiplication is only by autospores. The species is psychrophilic and is damaged at temperatures above 20 degree C. Hemichloris antarctica is a member of the cryptoendolithic microbial community living in porous sandstone rocks of the Antarctica cold desert. It inhabits the zone below that of cryptoendolithic lichens and survives at extremely low light intensities. In the natural habitat, morphology is somewhat different from that in culture, as chloroplasts are smaller and without articulation, and the cells develop a gelatinous sheath.

Antarctic Regions↗
PubMed1986

The Antarctic cold desert and the search for traces of life on Mars.

The cryptoendolithic microorganisms that live inside rocks in the frigid Ross Desert of Antarctica can serve as a terrestrial model for what may have happened to life forms on Mars when the planet became dry and cold. Trace fossils of microbial rock colonization exist in Antarctica, and similar structures could have formed on Mars. In some respects, such trace fossils could be an easier target for life-detection systems than fossils of cellular structures.

Adaptation, Biological↗
PubMed1985

Minimal metabolism, summit metabolism and plasma thyroxine in rodents from different environments.

Rodents were live-trapped in three environments (desert, intermediate and coastal) in Southern California, USA, chosen because of the taxonomic overlap of species. Upon capture, blood samples were taken and plasma thyroxine concentrations were measured. Four species (Dipodomys merriami, Perognathus fallax, Peromyscus eremicus and Peromyscus californicus) were returned to the laboratory for measurement of minimal and summit rates of metabolism. Heteromyid rodents had significantly lower plasma thyroxine concentrations (14-44 nmol l-1) than cricetid rodents (18-93 nmol l-1). Although there was significant habitat difference in plasma thyroxine levels, this influence was not constant between heteromyid and cricetid rodents. In most species, the desert individuals had the lowest plasma thyroxine concentration. Minimal metabolic rates were lower than expected in all four species, as well as in the tropical heteromyid Liomys salvini and summit metabolic rates were similarly reduced in all species. Upon capture there was considerable variation in plasma thyroxine concentration of different species (23-93 nmol l-1). However, following 10 weeks in captivity, the range and variability of plasma thyroxine levels in these species was considerably reduced (32-64 nmol l-1).

Animals↗
PubMed2006

Decay of cacti and carbon cycling.

Cacti contain large quantities of Ca-oxalate biominerals, with C derived from atmospheric CO(2). Their death releases these biominerals into the environment, which subsequently transform to calcite via a monohydrocalcite intermediate. Here, the fate of Ca-oxalates released by plants in arid environments is investigated. This novel and widespread form of biomineralization has unexpected consequences on C cycling and calcite accumulation in areas with large numbers of cacti. The magnitude of this mineralization is revealed by studying the large columnar cactus Carnegiea gigantea (Engelm.) Britton and Rose in southwestern Arizona (locally called the saguaro). A large C. gigantea contains on the order of 1 x 10(5) g of the Ca-oxalate weddellite-CaC(2)O(4) x 2H(2)O. In areas with high C. gigantea density, there is an estimated 40 g C(atm) m(-2) sequestered in Ca-oxalates. Following the death of the plant, the weddellite transforms to calcite on the order to 10-20 years. In areas with high saguaro density, there is an estimated release of up to 2.4 g calcite m(-2) year(-1) onto the desert soil. Similar transformation mechanisms occur with the Ca-oxalates that are abundant in the majority of cacti. Thus, the total atmospheric C returned to the soil of areas with a high number density of cacti is large, suggesting that there may be a significant long-term accumulation of atmospheric C in these soils derived from Ca-oxalate biominerals. These findings demonstrate that plant decay in arid environments may have locally significant impacts on the Ca and inorganic C cycles.

Arizona↗
PubMed1987

Microbial trace-fossil formation, biogenous, and abiotic weathering in the Antarctic cold desert.

In the Antarctic cold desert (Ross Desert), the survival of the cryptoendolithic microorganisms that colonize the near-surface layer of porous sandstone rocks depends on a precarious equilibrium of biological and geological factors. An unfavorable shift of this equilibrium results in death, and this may be followed by formation of trace fossils that preserve the characteristic iron-leaching pattern caused by microbial activity. Similar microbial trace fossil may exist in the geological record. If life ever arose on early Mars, similar processes may have occurred there and left recognizable traces.

Antarctic Regions↗
PubMed2003

Effects of starvation and desiccation on energy metabolism in desert and mesic Drosophila.

Energy availability can limit the ability of organisms to survive under stressful conditions. In Drosophila, laboratory experiments have revealed that energy storage patterns differ between populations selected for desiccation and starvation. This suggests that flies may use different sources of energy when exposed to these stresses, but the actual substrates used have not been examined. We measured lipid, carbohydrate, and protein content in 16 Drosophila species from arid and mesic habitats. In five species, we measured the rate at which each substrate was metabolized under starvation or desiccation stress. Rates of lipid and protein metabolism were similar during starvation and desiccation, but carbohydrate metabolism was several-fold higher during desiccation. Thus, total energy consumption was lower in starved flies than desiccated ones. Cactophilic Drosophila did not have greater initial amounts of reserves than mesic species, but may have lower metabolic rates that contribute to stress resistance.

Animals↗
PubMed1992

[New elements in organizing medical care for infectious patients in a mountainous desert locale with a hot climate].

In 1983-1985 the author of this article occupied the post of main infectionist of the 40th Army. During this period a number of new elements were elaborated by him to meet the requirements of medical care to infectious patients. At prehospital phase the nonorganic garrison isolators were deployed with 60-100 patient capacity on the basis of medical companies and separate medical battalions taking into account considerable delays in evacuation of patients. Lately it turned out more rational to deploy the infectious platoons in the organic structure of some medical companies and battalions. That made it possible to reduce the number of unfavourable cases. In addition to the existing structure of specialized medical care to the infectious patients it was planned to deploy 2-5 infectious units in military hospitals, deploy infectious hospitals with 200-500 patient capacity, boxes and intensive care units. The final recovery of convalescents was realized at the rehabilitation centre.

Afghanistan↗
PubMed1970

Multiplication of certain soil micro-organisms under simulated Martian conditions.

According to earlier observations, severe UV irradiation kills all micro-organisms in a chamber with simulated Martian conditions. However, even a thin soil layer protects buried micro-organisms from UV irradiation. The chief limiting factor for microbial multiplication under simulated Martian conditions seems to be soil humidity. Several micro-organisms were isolated from harsh environments (e.g., from Arctic, Antarctic desert and high-mountain soil samples). A strain of an oligonitrophilic mycococcus, isolated from Dixon Island, proved to be most resistant to low humidity. It multiplied in a mixture of limonite (maximal hygroscopical humidity 3.8%) + 2% (w/w) garden soil kept in a chamber simulating Martian conditions. Total cell count increased 7.6-fold and, in some experiments, 26-fold in 14 days. The oligonitrophilic mycococcus was able to grow even at a humidity level of 2.5%, that is less than maximal hygroscopical (3.8%). Under these conditions cell count increased 10-fold in 36 days. Thus, it was shown that even in Earth soils there are xerophytic micro-organisms which are able to multiply in limonite of low humidity. These data might correct our current concepts concerning microbial water requirements. One might speculate that Martian micro-organisms belong to xerophytic species.

Actinomycetales↗
PubMedDate not supplied

Abomasal nematodes in goats from the subtropical island of Grand Canary (Spain).

The prevalence of gastric nematodes in 151 goats on Grand Canary Island is around 56%, with a mean burden of 691 worms/animal. No significant differences of prevalence and intensity were found between the four isoclimatic areas of the island [dry-desert (DD); dry-steppe (DS); temperate-mild (TM); temperate-cold (TC)]. Five nematode species were identified, the most commonly-occurring being Teladorsagia circumcincta (observed in 65.8% of parasitized animals) and Trichostrongylus axei (51.9%). The distribution of the two species showed opposing trends: T circumcincta was more prevalent in the coastal areas (DD), diminishing in frequency closer to the centre of the island (TC), while the reverse was true of T axei. The other species identified were Haemonchus contortus, T trifurcata and Camelostrongylus mentulatus; their ranges were restricted to certain areas (H contortus in DS and TM; T trifurcata in DD, DS and TM; and C mentulatus in DD). To analyse the parasite association under natural conditions of an unusual nematode in goats, C mentulatus, with the usual parasites a principal component analysis (PCA) was used to assess the overall behaviour of the nematode community and to examine the Euclidean distances of the parasite associations. The mean Euclidean distances obtained for C mentulatus showed a tendency to a positive association which has also been observed for the other abomasal nematodes.

Abomasum↗
PubMed1985

The cryptoendolithic microbial environment in the Antarctic cold desert: temperature variations in nature.

In the Antarctic cold desert, cryptoendolithic microorganisms live under the surface of porous sandstone rocks. During the austral summer, the environment of the near-surface rock layers colonized by organisms is characterized by two kinds of temperature oscillations, both occurring across the freezing point. Low-frequency (diurnal) and large-amplitude (up to about 20 degrees C) oscillations on the sunlit surface of rocks result in a daily freeze-thaw cycle. This is a result of the diurnal changes in the sun altitude and angle with respect to the rock surface. The biological effect of this oscillation is the regulation of the onset and cessation of metabolic activity. The high-frequency (few minutes) oscillations occur only under certain weather conditions (sunny days with light winds) and are superimposed on the low-frequency oscillations. They are caused by the cooling effect of wind gusts on rock surfaces that are much warmer than ambient air temperatures. High-frequency oscillations result in a rapid freeze-thaw cycle on the surface, which, however, does not reach the microbial zone. These high-frequency freeze-thaw oscillations are probably the cause of the abiotic nature of the rock surface. Both oscillations seem to have an effect on rock weathering.

Air↗
PubMed2005

Seed germination and seedling emergence of three annuals growing on desert sand dunes in China.

BACKGROUND AND AIMS: Information on the initial growth characteristics of annuals found in Chinese deserts is very limited. The aim of this study was to investigate seed germination and interactive effects of irrigation and seed burial depth in sand on seedling emergence and seedling survival in three annuals (Agriophyllum squarrosum, Bassia dasyphylla and Aristida adscensionis) commonly growing on sand dunes in these regions. METHODS: Effects of temperature, light and polyethylene glycol-6000 on seed germination were examined by irrigating seeds sown on filter paper in Petri dishes. Seedling emergence was examined for seeds sown on the surface of, or at different depths (5, 10, 20, 30, 40 and 50 mm) in, sand-filled pots, which were irrigated under different regimes. For seeds buried at a depth of 50 mm, seed viability was examined after irrigation of the pots. KEY RESULTS: Seeds of three species germinated at most temperatures recorded between spring and autumn in their native habitats. No seed dormancy was found in any species. For all three species, seedling emergence was most favoured when seeds were buried at a depth of 10 mm. When seeds sown on the sand surface were irrigated, seed germination was considerably suppressed due to water deficiency, but many seeds remained viable. For A. squarrosum and B. dasyphylla, many seeds that were deeply buried and irrigated remained ungerminated but viable, while for A. adscensionis deeply buried seeds germinated, but the seedlings did not emerge due to unfavourable seedling growth in deep sand. CONCLUSIONS: Precipitation is the most crucial factor in determining the seasonal emergence of seedlings of the three tested species in the field. The vertical distribution of seeds in sand determines the proportion of seeds that germinate after precipitation and acts to maintain seed banks over multiple years.

Amaranthaceae↗
PubMed2006

Evolution of rattlesnakes (Viperidae; Crotalus) in the warm deserts of western North America shaped by Neogene vicariance and Quaternary climate change.

During Pleistocene, the Laurentide ice sheet rearranged and diversified biotic distributions in eastern North America, yet had minimal physical impact in western North America where lineage diversification is instead hypothesized to result from climatic changes. If Pleistocene climatic fluctuations impacted desert species, the latter would reflect patterns of restricted gene flow concomitant with indications of demographic bottlenecks. Accordingly, molecular evidence for refugia should be present within these distributions and for subsequent range expansions as conditions improved. We sought answers to these questions by evaluating mitochondrial DNA (mtDNA) sequences from four species of rattlesnakes [Crotalus mitchellii (speckled rattlesnake), Crotalus cerastes (sidewinder), Crotalus tigris (tiger rattlesnake), Crotalus ruber (red diamond rattlesnake)] with distributions restricted to desert regions of southwestern North America. We inferred relationships using parsimony and maximum likelihood, tested intraspecific clades for population expansions, applied an isolation-with-migration model to determine bi-directional migration rates (m) among regions, and inferred divergence times for species and clades by applying a semiparametric penalized likelihood approach to our molecular data. Evidence for significant range expansion was present in two of eight regions in two species (Crotalus mitchellii pyrrhus, C. tigris region north). Two species (C. cerastes, C. mitchellii) showed a distribution concomitant with northward displacement of Baja California from mainland México, followed by vicariant separation into subclades. Effects of Pleistocene climate fluctuations were found in the distributions of all four species. Three regional diversification patterns were identified: (i) shallow genetic diversity that resulted from Pleistocene climatic events (C. tigris, C. ruber); (ii) deep Pleistocene divisions indicating allopatric segregation of subclades within refugia (C. mitchellii, C. cerastes); and (iii) lineage diversifications that extended to Pliocene or Late Miocene (C. mitchellii, C. cerastes). Clade-diversifying and clade-constraining effects impacted the four species of rattlesnakes unequally. We found relatively high levels of molecular diversification in the two most broadly distributed species (C. mitchellii, C. cerastes), and lower levels of genetic diversification in the two species (C. tigris, C. ruber) whose ranges are relatively more restricted. Furthermore, in several cases, the distributions of subspecies were not congruent with our molecular information. We suggest regional conservation perspectives for southwestern deserts cannot rely upon subspecies as biodiversity surrogates, but must instead employ a molecular and deep historical perspective as a primary mechanism to frame biodiversity reserves within this region.

Adenosine Triphosphatases↗